Use of ultrasound imaging and heartbeat monitors to get "keepsake" images and videos is not entirely risk-free, the agency warns.

"Although there is a lack of evidence of any harm due to ultrasound imaging and heartbeat monitors, prudent use of these devices by trained health care providers is important," Shahram Vaezy, an FDA biomedical engineer, said in an agency news release.

"Ultrasound can heat tissues slightly, and in some cases, it can also produce very small bubbles [cavitation] in some tissues," Vaezy noted.

Because the long-term effects of tissue heating and cavitation are unknown, ultrasound scans should be done only when there is a medical need and only by professionally trained operators, the FDA said.

Several U.S. companies are in the business of making fetal keepsake videos from ultrasound imaging, the agency said.

In the absence of trained health professionals, there is no control on how long an imaging session will last, how many sessions will take place, or whether the ultrasound systems will be operated properly, the agency noted. In some cases, the ultrasound machine may be used for as long as an hour to get a video of the fetus.

The FDA also has concerns about over-the-counter sales and use of Doppler ultrasound heartbeat monitors, which are used to listen to the heartbeat of a fetus. These devices should only be used by, or under the supervision of, a health professional.

"When the product is purchased over the counter and used without consultation with a health care professional taking care of the pregnant woman, there is no oversight of how the device is used. Also, there is little or no medical benefit expected from the exposure," Vaezy said.

"Furthermore, the number of sessions or the length of a session in scanning a fetus is uncontrolled, and that increases the potential for harm to the fetus and eventually the mother," Vaezy added.

The agency acknowledged that "fetal imaging can promote bonding between the parents and the unborn baby," but said such opportunities are provided during routine prenatal care.